XRG is an open source system monitor for Mac OS X. XRG allows you to monitor CPU activity, memory usage, battery status, machine temperature, network activity, disk I/O, current weather, and stock market data. The goal of XRG is to be a functional system monitor that has a clean and flexible interface, so it doesn't intrude on the rest of your Mac experience. XRG is designed to take as little CPU time as possible while still showing detailed graphs on system usage. To give you an idea of XRG's overhead, it uses 3-5% of the CPU on a 667 Mhz G4, and 1-5% of the CPU on a Dual 1.25 Ghz G4.